path: root/subx/examples/ex12.subx

## example showing mmap syscall
# Create a new segment using mmap, save the address, write to it.
#
# To run (from the subx directory):
#   $ subx translate examples/ex12.subx -o examples/ex12
#   $ subx run examples/ex12
# You shouldn't get a segmentation fault.

== code
# instruction                     effective address                                                   operand     displacement    immediate
# op          subop               mod             rm32          base        index         scale       r32
# 1-3 bytes   3 bits              2 bits          3 bits        3 bits      3 bits        2 bits      2 bits      0/1/2/4 bytes   0/1/2/4 bytes

  # syscall(mmap, 0x1000)
  bb/copy-to-EBX  Mmap-new-segment/imm32
  b8/copy-to-EAX  0x5a/imm32/mmap
  cd/syscall  0x80/imm8

  # store to *EAX
  c7/copy                         0/mod/direct    0/rm32/EAX    .           .             .           .           .               0x34/imm32              # copy to *EAX

  # syscall(exit, EAX)
  89/copy                         3/mod/direct    3/rm32/EBX    .           .             .           0/r32/EAX   .               .                       # copy EAX to EBX
  b8/copy-to-EAX  1/imm32/exit
  cd/syscall  0x80/imm8

== data
# various constants used here were found in the Linux sources (search for file mman-common.h)
Mmap-new-segment:  # type mmap_arg_struct
  # addr
  00 00 00 00  # null
  # len
  00 01 00 00  # 0x1000
  # protection flags
  03 00 00 00  # PROT_READ | PROT_WRITE
  # sharing flags
  22 00 00 00  # MAP_PRIVATE | MAP_ANONYMOUS
  # fd
  ff ff ff ff  # -1 since MAP_ANONYMOUS is specified
  # offset
  00 00 00 00  # 0 since MAP_ANONYMOUS is specified

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